Forming threads in a workpiece by means of a tap is well known to include the steps of (1) drilling a properly sized hole in the workpiece and (2) turning a tap into the hole to form the threads. While the drilling operation is usually carried out by means of a machine such as a drill press, the tapping operation is usually carried out in the small shop by hand. A hand-driven precision tap is disclosed in the Harold Snow U.S. Pat. No. 4,702,131 issued Oct. 27, 1987. The snow tap comprises a wrench body having three crank handles extending radially therefrom.
It is highly desirable for accuracy to mount the tap in the machine used to perform the drilling operation without unclamping or moving the workpiece; this ensures that the tap is properly aligned with the axis of the drilled hole. The S. Ammatuna U.S. Pat. No. 3,653,780 granted Apr. 4, 1972 discloses a hand crank mechanism which addresses this desirable end result. The Ammatuna mechanism is complex and comprises a hand crank, a tap holder and an axially-expansible bias spring all of which fit within a drill press chuck.